ABSTRACT: Objective: This study was conducted to determine the incremental healthcare resource utilization (HRU) and costs associated with relapse or recurrence (R/R) in patients with major depressive disorder (MDD) treated with antidepressants (AD) in US clinical practice. Methods: In this retrospective cohort study, adult patients with MDD treated with a branded AD were selected from the Truven Health Analytics MarketScan Databases (January 1, 2004-March 31, 2015). Time to first indicator of R/R was described. Characteristics, HRU, and costs were compared between patients with and without R/R. Among patients with R/R, HRU and costs were also compared between the pre- and post-R/R period. Results: From the 22,236 selected patients, 5,541 had ? 1 indicator of R/R and 16,695 did not. The 3-year R/R rate varied between 21.3% and 36.4% based on pattern of AD use (continuous, switch/augmentation, or early discontinuation). Patients with and without R/R presented different characteristics-notably, more intensive prior AD use and a higher comorbidity burden. HRU and costs were high in both patients with and without R/R but substantially higher among those with R/R ($20,590 vs $12,368 per-patient-per-year (PPPY); adjusted difference [aDiff] = $7,037), mainly driven by increased inpatient (IP) services (adjusted incidence rate ratio IP days = 3.95; aDiff IP costs = $3,433 PPPY). Among patients with R/R, emergency department visits, IP days, and IP admissions were over 2-times higher during the post-R/R period and total costs increased by over 50% from $19,267 to $29,419 in the post-R/R period. Conclusions: The economic burden in MDD patients is substantial, but is significantly higher among those who experience R/R.